When a wind turbine generator or wind park connected to the utility grid in a point of common connection (PCC) experiences a disturbance on said grid e.g. a voltage drop, it always has a major impact on the operation and control of the wind turbine and/or wind park.
In order to support the grid during said disturbance, recent grid codes require that different power parameters is controlled according to the severeness of the grid disturbance.
Various methods have been suggested for controlling wind turbines during the grid disturbance. European patent no. EP 1 493 921 discloses an example of a method for controlling the phase angle between active and reactive power in dependency of measured voltage level.
A problem with the solutions of the above mentioned EP-patent is that it may not sufficiently support the utility grids during utility grid disturbances due to the complexity of said disturbances.
It is an object of the present invention to describe a flexible strategy for operating a wind turbine during a disturbance on the utility grid.